Boeing Co. grounded dozens of 737 Max jets to repair an electrical flaw that emerged in recently delivered models, forcing airlines to cancel flights and line up replacement aircraft.

U.S. carriers including Southwest Airlines Co., American Airlines Group Inc. and United Airlines Holdings Inc. parked a combined 67 of the workhorse planes Friday, about a third of the Max jets in service worldwide. The manufacturing glitch affects a subset of aircraft at 16 airlines, not the entire Max fleet, Boeing said in a statement.

The problem renews scrutiny of the upgraded 737 models as the manufacturer is counting on its best-selling jet’s comeback from the longest grounding in U.S. aviation history to help mend its battered finances. While analysts expect the affected planes to be flying within a few days, U.S. Transportation Secretary Pete Buttigieg underscored the stress on Boeing to ensure that its jets are safe.

“We need to make sure there’s full confidence before these specific aircraft return the air,” he said at a briefing. The Federal Aviation Administration will closely monitor the situation, he said.

The potential lapse “could affect the operation of a backup power control unit,” the FAA said in a statement. It is in contact with the airlines and Boeing “and will ensure the issue is addressed,” the agency said.

The electrical issue affects “only recently delivered aircraft,” a European Union Aviation Safety Agency spokesman said. “Boeing is currently implementing short- and long-term corrective actions to address the issue prior to resuming aircraft deliveries.”

Faded Luster

While the problem isn’t related to the flight-control system that was at the center of the Max’s nearly two-year grounding, it takes the luster off the comeback of Boeing’s most important product. U.S. regulators lifted the flying ban in November, clearing Boeing to resume delivering the jets for the first time since March 2019. The 737 provided a sales lift to the company, with a bumper commitment from Southwest, which had publicly flirted with a smaller single-aisle jet made by Airbus SE.

“The fix seems to be well understood and timing would depend on availability of technicians and equipment access,” Sheila Kahyaoglu, an analyst at Jefferies with a buy rating on the stock, wrote in a research note to clients. “Changing the equipment could take hours or days to fix, a modest disruption.”

Boeing fell 1.4 per cent to US$251.45 at 2:57 p.m. in New York, the second-sharpest drop on the Dow Jones Industrial Average. The shares had gained 19 per cent this year through Thursday, double the Dow’s increase.

The newest disclosure is the latest in a string of quality lapses and manufacturing flaws that have damaged Boeing’s reputation and afflicted its 787 Dreamliner, KC-46 military aerial tanker and Starliner spacecraft. The aerospace titan also has fired and sued a subcontractor on another high-profile project: turning two 747 jumbo jets into the next Air Force One fleet to haul U.S. presidents.

The electrical issue disclosed Friday was discovered by Boeing mechanics “on a production airplane during normal build activity,” according to a message to customers that was reviewed by Bloomberg. Operators were notified just hours after a separate email touting the growing number of flight hours and planes in service since the grounding ended.

The planemaker declined to say how many aircraft were affected of the 183 Max jets that have been put back into service since December. About 20 operators have been conducting about 400 daily flights, according to a separate memo.

“Boeing has traced the issue to a production change made in the installation process that occurred after our last aircraft was delivered before the fleet grounding in March 2019, which means 24 of our 737 Max aircraft are not affected by this issue,” David Seymour, American’s operations chief, said in a message to employees.

Boeing’s didn’t estimate how much time the repairs will require. “It could take a matter of hours or a few days,” said spokeswoman Jessica Kowal.

Airline Impact

Southwest said it pulled 30 Max 8 jets from its schedule, adding that it is flying only 15 of its 58 Max planes daily and expects “minimal” disruption to its operations. The Dallas-based carrier said it hadn’t experienced any operational problems related to the electrical issue.

American removed 17 Max planes from service, while United stopped flying 16. Alaska Air Group Inc. halted flights by all four of its Max aircraft.

The 737 Max, Boeing’s latest generation of the single-aisle aircraft, was grounded after two crashes killed 346 people within a five-month span. The jet was cleared to fly again by U.S. regulators in November, followed by regulators in Europe and most other major markets aside from China and India.